Dental repair material

ABSTRACT

The invention is directed to an improved dental composition useful in the repair of cavities, apex repairs, root perforations and root canals. Disclosed is a dental composition and dental composition additive which have improved handling characteristics, for example improved viscosity and setting time. The addition of effective amounts of a modified cellulose and calcium chloride to available dental repair compounds, such as mineral trioxide compound, results in the improved dental composition without affecting the other characteristics of the dental repair compound.

PARENT CASE TEXT

This application claims priority to Provisional U.S. Patent ApplicationNo. 60/693,268, which was filed on Jun. 23, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to dental repair materials. Specificallyimproved MTA (mineral trioxide aggregate) with improved handling andsealing properties.

2. Summary of the Related Art

Various compounds have been used as dental fill materials for cavitiesand root canal therapy. These include Amalgam, Reinforced ZincOxide-Eugenol (IRM and Super EBA), Composite Resins and Mineral TrioxideAggregate (MTA) and Portland Cement, herein after referred to generallyas “Dental Repair Compound”.

The attributes generally sought for root-end filling material includethe ability to 1) seal the apical portion in three dimensions, 2) bewell tolerated by the periradicular tissues with no inflammatoryreactions, 3) be non-toxic, 4) not promote, and preferably inhibit, thegrowth of pathogenic organisms, 5) stimulate the regeneration of normalrepiradicular tissues, 6) not be affected by moisture in either the setor unset state, 7) not be absorbable by the body within the confines ofthe tooth, but excess should be absorbable, 8) be dimensionally stableand should not expand, contract, or flow in any direction when set, 9)not corrode or be electrochemically active, 10) not stain the tooth orthe periradicular tissues, 11) be easy to mix and insert, 12) be easilydistinguishable on radiographs, and 13) adhere or bond to the toothwithout the need of undercuts.

MTA has been demonstrated to have diverse applications for all fields ofdentistry and appears to fulfill most characteristics of an ideal cementdue to its unique properties such as tissue compatibility, marginaladaptation, sealing ability, hydrophilic properties, and the capacity tostimulate hard tissue formation. These properties have allowed MTA to beindicated for the following endodontic procedures: Pulp Capping,Apexification, Perforation repair and other Miscellaneous uses.

Pulp Capping

In 1929, Hess reported a pulpotomy technique using calcium hydroxide.Until recently, these calcium hydroxide-based materials have foundwidespread use in traditional vital pulp therapy and have been themainstay for the protection of exposed dental pulps. The healing processof the dental pulp following a pulpotomy or a direct pulp cap ischaracterized by the formation of a hard tissue bridge with themaintenance of a vital subjacent pulp tissue free from chronicinflammatory cells. Recently, MTA has been approved by the FDA andrecommended for direct pulp capping. MTA's mechanism of action isthought to be similar to that of calcium hydroxide. MTA has calciumoxide that mixes with water to form calcium hydroxide. The reaction ofthe calcium from the calcium hydroxide with the carbon dioxide from thepulp tissue produces calcite crystals. These calcite crystals arethought to be the initiating factor in the induction of a hard tissuebarrier. Seux (1) observed a rich extracellular network of fibronectinin close contact with these crystals and concluded that both wereintegral in the initiating steps in the formation of a hard tissuebarrier. Tziafas (2) concluded that MTA was able to induce cytologicaland functional changes in pulpal cells, resulting in the formation offibrodentin at the surface of a mechanically exposed dental pulp.

Human studies have shown MTA to cause less pulpal hyperemia,inflammation, and necrosis when compared to calcium hydroxide. In astudy performed by Aeinehchi, (7) MTA induced a thicker dentinal bridgein third molars and was found to be associated with an intactodontoblastic layer more often than with calcium hydroxide. Additionalreasons MTA is an effective pulp capping material is its ability toeffectively seal the dentin-material interface to prevent bacterialcontamination, it is nonresorbable, proven biocompatibility, andbeneficial alkaline properties (25; 26; 27). Because of this, MTA isalso recommended for treatment of traumatically exposed pulps for thetreatment of complicated crown fractures (8).

Apexification

The traditional protocol in the treatment of necrotic immature teeth isthrough apexification using calcium hydroxide. In 1959, Granath was thefirst to describe the utilization of calcium hydroxide for apicalclosure. In 1966, Frank mainstreamed the apexification technique and wascredited as being the first to use this modality (9). This methodologyconsists of multiple appointments exchanging calcium hydroxide as theintracanal medicament to induce an apical hard tissue barrier ultimatelyto control the root canal filling material. The calcium hydroxide ischanged every 3 months until there is evidence of apical barrierformation. The most important problem with the classic apexificationtechnique with calcium hydroxide is the duration of therapy, which canlast from 3 to 24 months (9; 10). During this time frame the root canalis susceptible to reinfection due to the difficulty in maintaining atemporary restorative material that adequately seals the access opening.The root is also at risk to fracture due to the long treatment timerequired for apical barrier formation.

MTA treatment of these cases allows for a single treatment of immatureteeth as an option. The MTA apical plug technique, a one-step obturationafter short canal disinfection with calcium hydroxide is designated tocreate an artificial stop to the filling material. The physicalcharacteristics of MTA provide advantages over the traditional calciumhydroxide technique. MTA apexification cases can be restored inapproximately two weeks as opposed to traditional calcium hydroxidetherapy, which could take several months. MTA provides excellentmarginal adaptation to prevent leakage and the material isnon-resorbable. In 1996, Buchanan first recommended the use of MTA forone-appointment apexification by placing an apical matrix offreeze-dried demineralized bone followed by condensation of MTA (11).Witherspoon also recommends a technique for one-visit apexification.This technique advocates filling the apical to middle third with MTA,with the remainder of the canal system to be restored with a corematerial to reinforce the thin walls of the root (12). Giulianidescribed using MTA as an apical plug in teeth with necrotic pulps andopen apices. His technique advocated the use of calcium hydroxidetreatment for one week prior to placement of MTA as an apical plug withsubsequent obturation of the canal system. At recall, the clinicalsymptoms and teeth with periapical lesions had resolution within 6-12months (13). Hachmeister, in an MTA displacement study, concluded therewas a significant greater resistance to force with a 4 mm thickness ofMTA, regardless of calcium hydroxide use. Thus, the ideal recommendedthickness of the apical plug was shown to be 4 mm, in order to resistdisplacement of the material (14).

Perforation Repair

In dentistry, procedural accidents such as root or furcal perforationscan occur during root canal therapy, post space preparation, or as aconsequence of internal resorption. Studies have shown that theseperforations predispose periradicular tissues to chronic inflammationand promote the advancement of periodontal attachment loss, ultimatelycausing the loss of the tooth (15). Ingle reported that perforationswere the second greatest cause of endodontic failure and accounted for9.6% of all unsuccessful cases (16).

The repair of perforations can be problematic due to extrusion of therepair filling material, improper hemorrhage control, and the ability ofthe material to adequately seal the perforation site. MTA's uniquephysical characteristics allowing for superior marginal adaptation andsealing ability in hematic environments along with itsosteo/cementoconductive attributes make it an excellent material forperforation repair (28; 29; 30; 31). The inherent hydrophilic propertiesof MTA allow the repair material to set in a wet environment andadequately seal the perforation site. In 1993, Lee reported the first invitro study investigating the sealing ability of MTA for repair oflateral root perforations. The authors were able to demonstrate thatmoisture of the surrounding tissue acted as an activator of the chemicalreaction and did not pose a risk with its use in a moist environment.They were also able to demonstrate that overextrusion of the materialinto the perforation site occurred mostly in the IRM group, followed bythe amalgam group and then MTA. Lee concluded that the hydrophilicpowder absorbs moisture and allows for minimal condensation force, thusdecreasing the chance of overextrusion of the material (49). Sluykconcluded that the presence of moisture in the perforation site duringplacement was advantageous in aiding adaptation of MTA to the walls ofthe perforation (86).

Histologic repair of the perforation is possible with MTA. Pitt Ford etal. demonstrated using an in vitro canine model, that cementum has beenwas produced over MTA repairing perforations in the absence ofinflammation. Based on these results, Pitt Ford recommended the use ofMTA for immediate perforation repair (19). Holland also demonstrated noinflammation associated with repair of lateral root perforations withMTA over a 180 day observation period and that there was evidence ofcementum deposition in the majority of specimens (20). Recent studiesperformed to evaluate the clinical efficacy of MTA to seal both furcaland lateral perforations have only validated MTA as the material ofchoice in perforation repair (88-90).

Miscellaneous Uses

Additional uses for MTA have also been suggested. In a study performedby Cummings, MTA was compared to other materials and evaluated as anisolating barrier for internal bleaching. MTA demonstrated the leastamount of leakage compared to IRM and zinc phosphate. It was concludedthat this material can be used as an effective isolating barrier forinternal bleaching (21).

There have been several case reports documenting alternative uses forMTA. Hsiang-Chi presented a successful case report demonstrating therepair of perforating internal resorption with MTA. A partial pulpotomywas performed, and the material was placed adjacent to the exposed pulp.Teeth were extracted after 6 months. Histological exam of the teethshowed continuous dentin bridge formation without inflammation 6 monthsafter initial treatment (93). O'Sullivan (23), in another case report,demonstrated obturation of the canal system with MTA in a retainedprimary mandibular second molar where there was no succendaneous toothpresent. Eidelman et al. found clinical and radiographic success as adressing material following pulpotomy in primary teeth, suggesting MTAas a possible alternative to formocresol in primary teeth (24).

Presently, dental materials, such as e.g., MTA, Portland cement, aredifficult to handle due to viscosity and slow setting times. Thesematerials have low viscosity and therefore require special equipment toadminister into small or tortuous areas in the patient's mouth.

U.S. Pat. Nos. 5,415,547, and 5,769,638 titled “Tooth Filling Materialand Method of Use.” Teach the use of Portland Cement as a dental repairmaterial for apicoectomy, a tooth cavity, correction of rootperforation. Those patents also teach a method of performing aapicoectomy, a method for filling teeth and a method for sealing rootperforations. It has also been observed that Portland Cement has similarpropteties to MTA as a dental repair compound.

International Patent Application WO 2005/039509 A1, titled “A DentalComposite Material and Uses Thereof.” Teaches using a viscosityenhancing additive in Portland Cement. The application also teachesusing the same viscosity enhancing substance to improve MTA as aworkable dental repair material. However the description suggestedenhancement of MTA. The viscosity enhancing substance is Polyvinlyalcohol, cellulose, cellulose derivatives, polyethylene oxide, naturalgums, and/or aqueous clay dispersion.

The following references are cited throughout this section using therelated parenthetical numbering system. The references are incorporatedherein by reference. Applicant reserves the right to challenge theveracity of statements made therein.

1) Seux D, Regad C, Magloire H, Holz J. A model of an in vitrobiological assay controlled by immunofluorescence and scanning electronmicroscopy. J Biol Buccale. 1991;19:147-53.

2) Tziafas D, Pantelidou O, Alvanou A, Belibasakis G, Papadimitriou S.The dentinogenic effect of mineral trioxide aggregate (MTA) inshort-term capping experiments. Int Endod J 2002;35:245-54.

3) Pitt Ford T R, Torabinejad M, Abedi H R, Bakland L K, Kariyawasam SP. Using mineral trioxide aggregate as a pulp-capping material. J AmDent Assoc 1996;127:1491-4.

4) Faraco I M, Jr., Holland R. Response of the pulp of dogs to cappingwith mineral trioxide aggregate or a calcium hydroxide cement. DentTraumatol 2001;17:163-6.

5) Junn D J, McMillan P, Bakland L K, Torabinejad M. Quantitativeassessment of dentin bridge formation following pulp capping withMineral Trioxide Aggregate (MTA).[Abstract #29] J Endod 1998;24:278.

6) Dominguez M S, Witherspoon D E, Gutmann J L, Opperman L A.Histological and scanning electron microscopy assessment of variousvital pulp-therapy materials. J Endod 2003;29:324-33.

7) Aeinehchi M, Eslami B, Ghanbariha M, Saffar A S. Mineral trioxideaggregate (MTA) and calcium hydroxide as pulp-capping agents in humanteeth: a preliminary report. Int Endod J 2003;36:225-31.

8) Bakland L K. Management of traumatically injured pulps in immatureteeth using MTA. J Calif Dent Assoc 2000;28:855-8.

9) Frank A. Therapy for the divergent pulpless tooth by continued apicalformation. J Am Dent Assoc 1966;72:87-93.

11) Buchanan L S. One-visit endodontics: a new model of reality. DentToday 1996; 15:36, 8, 40-3.

12) Witherspoon D E, Ham K. One-visit apexification: technique forinducing root-end barrier formation in apical closures. Pract ProcedAesthet Dent 2001; 13:455-60.

13) Giuliani V, Baccetti T, Pace R, Pagavino G. The use of MTA in teethwith necrotic pulps and open apices. Dent Traumatol 2002;1 8:217-21.

14) Hachmeister D R, Schindler W G, Walker W A, 3rd, Thomas D D. Thesealing ability and retention characteristics of mineral trioxideaggregate in a model of apexification. J Endod 2002;28:386-90.

15) Seltzer S, Sinai I, August D. Periodontal effects of rootperforations before and during endodontic procedures. J Dent Res.1970;49:332-9.

16) Ingle J I. A standardized endodontic technique utilizing newlydesigned instruments and filling materials. Oral Surg Oral Med OralPathol. 1961;14:83-91.

17) Lee S J, Monsef M, Torabinejad M. Sealing ability of a mineraltrioxide aggregate for repair of lateral root perforations. J Endod1993;19:541-4.

18) Sluyk S R, Moon P C, Hartwell G R. Evaluation of setting propertiesand retention characteristics of mineral trioxide aggregate when used asa furcation perforation repair material. J Endod. 1998;24:768-71.

19) Pitt Ford T R, Andreasen J O, Dorn S O, Kariyawasam S P. Effect ofvarious zinc oxide materials as root-end fillings on healing afterreplantation. Int Endod J 1995;28:273-8.

20) Holland R, Filho J A, de Souza V, Nery M J, Bemabe P F, Junior E D.Mineral trioxide aggregate repair of lateral root perforations. J Endod.2001 ;27:281-4.

21) Cummings G R, Torabinajad M. Mineral Trioxide Aggregate (MTA) as anisolating barrier for internal bleaching. [Abstract #53] J Endod.1995;21:228.

22) Hsieng H C, Cheng Y A, Lee Y L, Lan W H, Lin C P. Repair ofperforating internal resorption with mineral trioxide aggregate: a casereport. J Endod. 2003;29:538-9.

23) O'Sullivan S M, Hartwell G R. Obturation of a retained primarymandibular second molar using mineral trioxide aggregate: a case report.J Endod. 2001 ;27:703-5.

24) Eidelman E, Holan G, Fuks A B. Mineral trioxide aggregate vs.formocresol in pulpotomized primary molars: a preliminary report.Pediatr Dent. 2001;23:15-8.

25) Torabinejad M, Watson T F, Pitt Ford T R. Sealing ability of amineral trioxide aggregate when used as a root end filling material. JEndod. 1993;19:591-5.

26) Torabinejad M, Pitt Ford T R, McKendry D J, Abedi H R, Miller D A,Kariyawasam S P. Histologic assessment of mineral trioxide aggregate asa root-end filling in monkeys. J Endod 1997;23:225-8.

27) Torabinejad M, Hong C U, McDonald F, Pitt Ford T R. Physical andchemical properties of a new root-end filling material. J Endod 1995;21:349-53.

28) Pitt Ford T R, Torabinejad M, McKendry D J, Hong C U, Kariyawasam SP. Use of mineral trioxide aggregate for repair of furcal perforations.Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:756-63.

29) Koh E T, Torabinejad M, Pitt Ford T R, Brady K, McDonald F. Mineraltrioxide aggregate stimulates a biological response in humanosteoblasts. J Biomed Mater Res. 1997;37:432-9.

30) Moretton T R, Brown C E, Jr., Legan J J, Kafrawy A H. Tissuereactions after subcutaneous and intraosseous implantation of mineraltrioxide aggregate and ethoxybenzoic acid cement. J Biomed Mater Res2000;52:528-33.

31) Thompson T S, Berry J E, Somerman M J, Kirkwood K L. Cementoblastsmaintain expression of osteocalcin in the presence of mineral trioxideaggregate. J Endod 2003;29:407-12.

SUMMARY OF THE INVENTION

The inventors have made the surprising discovery that the addition ofdivalent-cationic halogen salt and derivatives of cellulose polymers todental repair compounds results in dental repair compositions havingimproved handling properties, which enables more effective treatment ofvarious indications of use. Those improved handling properties includeincreased viscosity and shortened setting time. Thus, the invention isdirected to compositions, treatment methods, and manufacturing processesfor improved dental repair compositions and dental repair procedures.

In one embodiment, the invention is drawn to a dental repaircomposition, comprising a dental repair compound, such as for examplebut not limited to Portland cement and mineral trioxide aggregate(“MTA”), a divalent cation halogen salt (e.g., calcium chloride,magnesium chloride, and the like), and a polymer thickening agent, suchas a cellulose derivative polymer like methyl-cellulose or the like. Ina preferred aspect, the divalent cation halogen salt is calcium chlorideand the polymer thickening agent is methyl-cellulose. However, theinventors envision that other salts and polymers, which have similarproperties to CaCl₂ and methyl-cellulose, may also be used as additivesto the dental repair compounds to produce the same improved handlingproperties (supra). Concentration ranges for the divalent cation halogensalt can be from as low as 0.1% by weight to as high as 20% by weight.Likewise, the concentration range for the polymer thickener can be fromas low as 0.1% by weight to as high as 20% by weight. In a morepreferred embodiment, the salt is CaCl₂ at a concentration ofapproximately 2% by weight and the polymer thickener is methyl-celluloseat a concentration of approximately 1%. However, the inventors envisionthat the relative amounts of CaCl₂ and methyl-cellulose may be alteredoutside of these ranges and values, so long as the therapeuticproperties of the dental repair compound are not significantlycompromised.

In another embodiment, the invention is drawn to a compound additive,which can be added to a dental repair compound (supra). The compoundadditive is a gel or solution that consists essentially of the divalentcation halogen salt and polymer thickening agent. To produce theimproved dental repair composition, the practitioner would mix thecompound additive with the dental repair compound to produce the workingimproved dental repair composition prior to application to the patient.Preferably, the compound additive consists essentially of CaCl₂ andmethyl-cellulose, both of which are represented at concentrations higherthan their respective final concentrations in the working improveddental repair composition.

In another embodiment, the invention is drawn to methods of producingthe improved dental repair composition and compound additives (supra).In one particular preferred aspect, calcium chloride is weighed out inan amount representing approximately 2% of the final composition weight.The calcium chloride is added to water for a 3:1 powder to water ratio(by weight). The solution can be divided in half, half of which isheated to 80° C. The methyl-cellulose is weighed out in an amountrepresenting approximately 1% or 2% of the final composition weight. Themethyl-cellulose is added to the half of the calcium chloride solutionthat was heated to 80° C.

To this mixture, the other half of the calcium chloride solution (atroom temperature) is added to the warm solution and stirred until all ofthe solid material is in solution. This mixture is then chilled to 0° C.to allow the mixture to thicken. The solution is stirred for about 30minutes to produce a homogeneous gel. This gel is a compound additive,which may then be added to the dental repair compound (e.g., MTA,Portland cement) to produce the improved dental repair composition.

In another embodiment, the invention is drawn to methods of effectingdental repairs using the improved dental repair compositions described(supra). Those dental repairs include but are not limited to filling atooth cavity, treating tooth decay, performing root canal therapy,apicoectomy, and sealing a root perforation.

In yet another embodiment, the invention is drawn to a kit useful in thepractice of dental repair, said kit comprising a packaged dental repaircompound (e.g., Portland cement, MTA), a packaged compound additive(supra), and a set of instructions describing how to mix (e.g., in whatproportions) the dental repair compound and compound additive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Root-end filling diagrams and evaluation scores: which 0=no dyepenetration observed, 1=dye penetration observed up to ½ of the cavitydepth, 2=dye penetration observed between ½ but not beyond root-endfilling material placement, 3=dye penetration observed beyond thefilling material and into the canal system.

FIG. 2. depicts the chemical shrinkage apparatus

FIG. 3. depicts the receiving container and washout apparatus.

FIG. 4 depicts methylene blue penetration beyond the material dentininterface for amalgam.

FIG. 5 shows no methylene blue penetration noted for MTA.

FIG. 6 shows no methylene blue penetration noted for CMMTA.

FIG. 7 shows the graph illustrating the chemical shrinkage over 168hours for samples 1 through 6.

FIG. 8 shows the Graph Illustrating the chemical shrinkage over 8 hoursfor samples 1 through 6.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The following example discloses a single preferred embodiment of theinvention. It is meant merely to illustrate the invention and not tolimit the invention. The skilled artisan in the practice of thisinvention will readily recognize that substitutions and alterations canbe made while remaining within the metes and bounds of the invention,which are set forth in the claims that follow.

Recently, the inventors herein demonstrate improved characteristics ofMTA (ProRoot® Dentsply Tulsa Dental, Tulsa, Okla.) through the additionof 1% methylcellulose (MC) and 2% calcium chloride (CaCl₂) into itsparent cement. The inventors observed that the handling characteristicswere vastly improved while the compressive strength of MTA with theadditives was not significantly affected and the setting time of MTAwith the additives was significantly shorter than the MTA control. Thisobservation also brought about questions on whether the chemicaladditives have significantly altered any inherent physical propertiescrucial to MTA's success as an ideal dental cement. Therefore, thisexample describes the physical properties, (marginal leakage, chemicalshrinkage, cement solubility, and washout resistance) of chemicallymodified MTA (1% MC+2% CaCl₂ in MTA/H₂O) and compare it to unalteredMTA.

Four different tests were designed and employed to assess marginalleakage, chemical shrinkage, cement solubility, and washout resistancebetween the unaltered MTA and chemically modified MTA (CMMTA) to ensurethat the added chemicals have not deteriorated the aforementionedproperties of MTA.

Dye leakage results demonstrated no significant difference between CMMTAand MTA samples. In addition, there was significantly less leakagebetween the CMMTA and MTA groups compared to amalgam. Chemical shrinkageresults reported no significant difference between any of the groups(1-6) at any of the designated timeframes (T₁, T₂, T₃, T₂₄, and T_(w)).More importantly, there was no significant difference in mean chemicalshrinkage between CMMTA and MTA samples at any of the designated timeintervals of the specimens. Cement solubility results revealed nosignificant difference between CMMTA and MTA groups. Furthermore,results demonstrated no significant difference between weights of thetest materials at any designated time intervals (T₁,T₇,T₂₁). Modifiedwashout tests indicated a significant difference observed between groups1-3. However, there were no significant differences noted between CMMTAand MTA groups.

In conclusion, the data presented in this research confirm that theaddition of 1% MC+2% CaCl₂ into MTA does not deleteriously alter any ofthe parent cement's physical properties (marginal leakage, chemicalshrinkage, cement solubility, and washout resistance) and that CMMTAperformed as well or better than MTA in all of the above testsconducted.

EXAMPLE Modified MTA

As of 2005, there have been some 150 articles published regardingMineral Trioxide Aggregate's (MTA) composition, properties,biocompatibility, and indications for use. MTA has become the materialof choice for an array of endodontic applications, including vital pulptherapy, apexification, perforation repair, as well as a root-endfilling material. Any root-end filling material should have the abilityto seal the root canal from bacterial and chemical invasion as well asbe biocompatible, prevent periradicular tissue irritation, and ideallyfavor regeneration of the involved tissues to their prediseased status(1).

MTA has been demonstrated to meet many of the ideal properties of aroot-end filling material as described by Gartner and Dom (2). MTA isdifferent from other root-end filling materials currently in use,(Super-EBA, IRM, Amalgam, and composite resin-based materials). Both invitro and in vivo studies have consistently demonstrated this materialto be equal or superior in terms of its biocompatibility (3-9), marginaladaptation (10) and sealing abilities, (11-13), even in the presence ofblood and moisture (14).

MTA is a chemical mixture of three powder ingredients: Portland cement(75%), bismuth oxide (20%), and gypsum (5%) (15). These powders consistsof fine trioxides and other hydrophilic particles, that upon mixing withsterile water, results in a wet, sandy consistency that sets in thepresence of moisture in approximately 165 minutes. Hydration of thepowder results in the formation of a colloidal gel with an initialsetting pH of 10.2, which increases to 12.5 after 180 minutes. Anelemental analysis of MTA revealed an overall composition of MTA as58.9% Ca, 20.1% Bi, 9.4% Si, 2.1% Al, 2.7% S, 4.4% Fe, with traceamounts of Cr, Ni, and Pb (16).

The unique composition of MTA often makes it hard to use, especially inregions with difficult access. According to Lee (17), MTA is a difficultmaterial to handle due to its granular consistency, slow setting time,and initial looseness. Once the mixture starts to dry, it looses itscohesiveness and becomes unmanageable. Delivery of MTA has focusedmainly on carrier and syringable-type devices to simplify placement ofthe material, however, each still has its own set of problems. Thedevices can become easily clogged and can be difficult to use due tolocation and access of the surgical site.

Recent modifications to MTA has been studied and shown to improve thehandling characteristics (18). 1% methylcellulose (MC) was added as ananti-washout additive to enhance handling characteristics and provide amore cohesive user-friendly material. This additive does have drawbacks,including decreased compressive strength due to voids entrapped in thecement and longer setting times. To offset these drawbacks, 2% CaCl₂ wasincorporated as an accelerator to decrease the setting time. Theinventors observed that the compressive strength with the additives wasnot significantly affected compared to MTA at 24 hours and 3 weeks(Table 1) while setting time of MTA with the additives was significantlyshorter than the MTA control (Table 2). TABLE 1 Compressive strength 24hrs 3 wks 1% MC + 2% CaCl₂ in MTA 25.5 ± 4 MPa  29.1 ± 6.4 MPa MTA(control) 26.4 ± 6 MPa 30.4 ± 12.8 MPa

TABLE 2 Setting time Minutes 1% MC + 2% CaCl₂ in MTA  57 ± 3 MTA(control) 202 ± 3

Materials and Methods

All chemically modified MTA (CMMTA) samples were prepared as describedby Ber (18). Briefly, CaCl₂ (PCCA, Houston, Tex.) equal to 2% of thesample weight was added to distilled water and mixed into solution. Halfof the solution was placed on a hot plate were the temperature of thesolution was raised to 80° C. 1% MC (Sigma, St. Louis, Mo.) was added tothe warmed solution and stirred to wet the particles. The remainder ofthe room temperature solution was added and then stirred until all ofthe powder was in solution. It was then stored at 0° C. for 20 minutesto allow for the mixture to thicken. The solution was then mechanicallystirred for 30 minutes to create a homogenous gel. This solution wasthen added to MTA at a 0.33 water/cement ratio generate a chemicallymodified MTA cement. All conventional MTA samples were mixed withdistilled water according to manufacturer's instructions, using a powderto water ratio of 3:1.

Dye Leakage

Forty-one extracted, human, single-rooted maxillary incisors werecollected and stored in 10% formalin. The clinical crowns weredecoronated at the cementoenamel junction (CEJ) with a #557 carbide burin a highspeed handpiece with water coolant. Working length wasdetermined by subtracting 0.5 mm from the length at which a #10 K fileexited the apical foramen. Teeth were prepared using rotaryinstrumentation to a master apical file ( IAF) size 40/04 withnickel-titanium (NiTi) ProFile (Tulsa Dental Products, Tulsa, Okla.)instruments via modified crown-down technique in conjunction with RCPrep (Premier, King of Prussia, Pa.) and 5.25% NaOCl⁻ (Clorox; CloroxCo., Oakland Calif.). The canals were dried with paper points andsamples were obturated immediately with Roth Root Canal Cement 801 Elitegrade (Roth International Ltd., Chicago, Ill.) and thermoplasticizedgutta-percha utilizing an Obtura II (Obtura/Spartan USA, Fenton, Mo.)unit set at 200° C. and expressed in one continuous movement. Canalswere then compacted with an S Kondensor plugger (Obtura/Spartan USA,Fenton, Mo.) and coronal access openings sealed with IRM (ID Caulk,Milford, Del.).

All roots were then stored at 37° C. and 100% humidity for 1 week.Apical root resections were performed on all roots by removing 3 mm ofeach apex at 90 degrees to the long axis of the tooth with a #169fissure bur using a highspeed handpiece with water coolant. A 3 mmroot-end cavity preparation was performed using ultrasonics (SpartanUSA, Fenton, Mo.) and KIS tips (Obtura/Spartan USA, Fenton, Mo.) undersurgical microscope (Global Surgical Corp., St. Louis, Mo.) at 9×magnification. Two coats of nail polish were applied to the entiresurface of each root except where the root-end filling was to be placed.

Teeth were randomly assigned to two groups of 15 roots each. Group 1 wasretrofilled with MTA (ProRoot®, Dentsply Tulsa Dental, Tulsa, Okla.).Group 2 with chemically modified MTA, (1% MC+2% CaCl₂ in MTA). Anadditional 5 roots (Group 3) were filled with high copper amalgam (TytinAmalgam, Kerr Mfg. Co., Romulus, Mich.) without cavity varnish. Eachmaterial was condensed into their respective preparation sites using anS Kondensor plugger. Three instrumented roots with retrogradepreparations and no root-end fillings served as positive controls whilethree roots were instrumented and obturated with gutta-percha andsealer. Entire root surfaces covered with two coats of nail polish wereused as negative controls.

All roots were then stored in 1% methylene blue for 72 hours. The rootswere rinsed with distilled water and nail polish removed. Teeth weresectioned buccolingually using a 169 tapered fissure bur in a highspeedhandpiece and fractured using a Woodson instrument. Dye penetration wasevaluated under surgical microscope (Global Surgical Corp., St. Louis,Mo.) at 9× magnification.

The presence of dye penetration through the material/dentin interfacewas scored on a four-point scale as shown in FIG. 1, in which 0=no dyepenetration observed, 1=dye penetration observed up to 1 of the root-endfilling material, 2=dye penetration observed between ½ but not beyondthe root-end filling material, 3=dye penetration observed beyond theroot-end filling material and into the canal system. Results wererecorded and submitted to non-parametric Kruskal-Wallis and Mann-WhitneyU-tests.

Chemical Shrinkage

The chemical shrinkage methodology was based on the original workperformed by Geiker (19). Modification to Geiker's original work iscurrently under proposal as the protocol designated to determinechemical shrinkage of Portland cement for the cement industry,(ASTMCXXXX Test Method for Chemical Shrinkage of Hydraulic Cement Paste)(20). All cement pastes were prepared in accordance to manufacturer'sinstructions at a 0.33 water/cement ratio for groups 1-6 (Group1=PC/H₂O, Group 2=CMMTA, Group 3=MTA/H₂O, Group 4=2% CaCl₂ in MTA, Group5=2% CaCl₂ in Portland cement, and Group 6=1% MC+2% CaCl₂ in Portlandcement). The mass of each empty glass vial (diameter=2.5 cm and height=6cm) was determined to the nearest 0.01 g. Ten grams of cement paste wasplaced in the bottom of each vial using a vibrating table to achieve apaste height between 5 mm and 10 mm in the vial. Mass of the glass vialwas determined with the consolidated cement paste to the nearest 0.0001g. The remainder of the glass vial was then filled to the top withde-aerated water and sealed with a rubber stopper encasing a pipettegraduated in 0.01 ml increments. The respective graduated pipette wasthen filled to the top with de-aerated water with the addition of 1-2drops of hydraulic oil to minimize the evaporative process over the1-week timeframe (FIG. 2). Mass of the vial+capillary tube filled withwater and cement paste was immediately determined to the nearest 0.0001g. The vial was then transferred and placed in a constant temperaturewater bath of 23.0±0.5° C. At 30 minutes (T_(30m)), the glass vial wasthen removed from the water bath, wiped dry, capillary tube filled toexcess with de-aerated water, and mass determined to the nearest 0.0001g. Additional weight measurements were taken at hourly intervals for thefirst 8 hours (T_(1h)-T_(8h)) followed by additional measurements at 24hours (T_(24h)) and 1 week (T_(168h)) respectively. Calculation of themass sample was determined as follows:

-   -   The mass of cement powder in the vial is given by:        $M_{cement} = \frac{\left( {M_{{vial} + {paste}} - M_{vialempty}} \right)}{\left( {1.0 + \frac{w}{c}} \right)}$    -   M_(cement)=mass of cement in the vial (g)    -   M_(vial+paste)=mass of the glass vial with the added cement        paste (g)    -   M_(vialempty)=mass of the empty vial (g)    -   w/c=water-cement ratio by mass of the prepared paste (0.33)

Once the mass of the cement was calculated, this weight in grams wasincorporated into the following formula to determine the chemicalshrinkage per unit mass at the specific time interval.

-   -   The chemical shrinkage per unit mass of cement at time t is        computed as:        ${{CS}(t)} = {{\left( \frac{\left\lbrack {{M(t)} - {M\left( {30\quad\min} \right)}} \right\rbrack}{M_{cement}} \right)/\rho}\quad W}$    -   CS(t)=chemical shrinkage at time t (mL/g cement)    -   M(t)=mass of filled density bottle at time t (g)    -   pW=density of water (mL/g) (0.99754 at 23° C.)    -   M(30 min)=Mass of cement paste at T_(30m)

To briefly summarize, two 10 gram specimens were run for each cementgroup (Group 1=PC/H₂₀, Group 2=CMMTA, Group 3=MTA/H₂O, Group 4=2% CaCl₂in MTA, Group 5=2% CaCl₂ in Portland cement and Group 6=1% MC+2% CaCl₂in PC) at a 0.33 water/cement ratio. Weight measurements (0.0001 g) weretaken from the shrinkage apparatus initially at 30 minutes (T_(30m))followed by hourly intervals for the first 8 hours (T_(1h)-T_(8h)).Subsequent weighing of samples were taken at 24 hours (T_(24h)) and 1week (T_(168h)) respectively with the resulting average of each groupbeing reported and statistically examined for differences in chemicalshrinkage per unit mass between groups at the aforementioned specifiedtime intervals (T_(1h), T_(2h), T_(3h), T_(24h), and T_(168h)).

Solubility

Degree of solubility of the test samples was determined by the modifiedmethod of ADA/ANSI specification #30 (21) as performed by Torabinejad etal. (22). Briefly, the materials were prepared in accordance tomanufacturer's recommendations. Individual MTA and CMMTA samples werehand-mixed and transferred into a small disc approximately 20 mm×1.5 mmby use of a plastic former and two glass slabs. Mixing and weighing ofthe samples were performed by a single operator at 23.0±2° C. and arelative humidity of 50±5%. 6 discs of MTA and 8 discs of CMMTA wereprepared and tested. Following fabrication, discs were placed in 100%humidity for 21 hours. Discs were removed and stored individually inglass jars containing 50 ml of distilled water at 37° C. The specimenswere then desiccated for 1 hour at 37° C. Individual discs were weighedto the nearest 0.0001 g and placed back into their respective glassjars. The water in glass jars were neither changed nor added during thetest periods. Desiccation and weighing of samples were performed at: 1day (T₁), 7 days (T₇) and at 21 days (T₂₁). Mean weights of thespecimens were recorded and submitted to non-parametric Kruskal-Wallisand Mann-Whitney U-tests to determine statistical differences betweenweights of the test materials at different time intervals.

Dispersion Resistance/Washout

The percentage of cement washout of the test samples was determined by amodified method based on concrete standard test (CRD-C 61-89A) (24). Thereceiving container and washout apparatus is shown in FIG. 3. Briefly,two representative 10 gram samples from each group (Group1=Portlandcement, Group2=MTA, Group3=CMMTA) were prepared in accordance tomanufacturer's instructions at a 0.33 water/cement ratio. Each samplewas hand-mixed and placed into a separate receiving container. Thecement mixture was tamped down with the handle of a cement spatula 10-15times to allow the cement to adhere to the walls of the container.Extruded cement was removed from the outside of the receiving containerallowing the mass of the cement and container to be obtained andrecorded to the nearest 0.0001 g (M_(i)). Immediately following weightmeasurement, the receiving container with cement sample was allowed tofreely fall through the H₂O to the bottom of a 1000 ml graduatedcylinder and sit for 15 seconds. The receiving container was then slowlyraised to the top of the graduated cylinder in 5±1 seconds, allowed todrain for 2 minutes, air dried carefully to remove excess H₂O but notdisrupt the cement, and weighed to the nearest 0.0001 g. Mass of thecement remaining in the receiving container was recorded as M_(f).Repeated testing was performed three times on the same cement sample,determining a new M_(f) each time. The M_(f) after the final sequencewas then calculated as the cumulative loss in mass qualifying as thepercent washout of the cement (D) demonstrated below.

-   -   The washout of the cement is computed as:        $D = {\frac{M_{i} - M_{f}}{M_{i}} \times 100}$    -   D=washout %    -   M_(i)=mass of sample before initial test    -   M_(f)=mass of sample after each test        Results

Dye Leakage

Microleakage results of all groups are presented in Table 1. Resultsfrom group 1 (MTA) showed that 14 of 15 samples (93%) showed anevaluation score of 0 (no leakage) (FIG. 5). From group 2 (CMMTA), 100%of the specimens displayed an evaluation score of 0 (no leakage) (FIG.6). In contrast, 100% of the samples from group 3 (amalgam) displayed anevaluation score of 3 (dye penetration throughout the entire canal). TheKruskal-Wallis test was used to compare differences between all groups.This test revealed a significant difference between the groups (P<0.05).When examining differences within groups, the Mann-Whitney U-test showedthat leakage observed in Group 1 (MTA) was significantly less (P<0.05)than Group 3 (amalgam). Likewise, Group 2 (CMMTA) displayedsignificantly less leakage (P<0.05) than Group 3. There was nosignificant difference noted between Groups 1 (MTA) and 2 (CMMTA)(P<0.05). Positive control samples showed dye leakage throughout theentire canal system, while the negative control samples displayed nosigns of dye penetration. TABLE 3 Results for root-end fillingmaterials. Evaluation Scores Material No. of samples 0 1 2 3 MTA/H2O(Group 1) 15 14 0 0 1 CMMTA (Group 2) 15 15 0 0 0 Amalgam (Group3) 5 0 00 5 Positive control† 3 0 0 0 3 Negative control‡ 3 3 0 0 0†Instrumented roots obturated with gutta-percha and sealer; retrogradepreparations with no root-end fillings.‡Instrumented roots obturated with gutta-percha and sealer; entire rootsurfaces covered with two coats of nail polish.

Chemical Shrinkage

Results from the Kruskal-Wallis test confirmed our rationale andrevealed that there was no significant difference noted between groups1-6 (P<0.05). Furthermore, statistical analysis employed with Mediantests to compare groups at the designated time intervals (T_(1h),T_(2h), T_(3h), T_(24h), and T_(168h)) were unable to show astatistically significant difference in mean chemical shrinkage betweenthe specimens at the previously mentioned time frames (P<0.05).

In this experiment, we were interested in the amount of shrinkage thatwould occur from time T_(30m) to time intervals T_(1h), T_(2h), T_(3h),T_(24h), and T_(168h). Reasoning for these timeframes was that therecommended setting time for MTA is 165 minutes (22). Thus, it isexpected that the majority of hydration would be occurring during theinitial three hours for MTA and therefore, chemical shrinkage of thecement would be anticipated to be at its greatest. ASTM guidelines forthis experiment require hourly measurements for the first 8 hours, a 24hour reading, and finally at 1 week.

Graph illustrating chemical shrinkage over 8 hours for samples 1-6.

Solubility

The mean weights (g) of the specimens and standard deviation for eachtest material at various time intervals (T₁, T₇, T₂₁,) are shown inTables 2 and 3. TABLE 4 Chemically Modified MTA Solubility Results CMMTAWo (Initial Total Change in weight) T₁ T₇ T₂₁ Mass (To-T₂₁) Sample 10.8925 g 0.8991 g 0.9009 g 0.9075 g (+)1.68% Sample 2 0.9479 g 0.9528 g0.9553 g 0.9640 g (+)1.69% Sample 3 0.9727 g 0.9888 g 0.9899 g 0.9966 g(+)1.66% Sample 4 0.7681 g 0.7759 g 0.7730 g 0.7756 g (+)2.46% Sample 50.9800 g 0.9720 g 0.9861 g 0.9850 g (+)0.51% Sample 6 0.8814 g 0.8819 g0.8896 g 0.8857 g (+)0.49% Sample 7 0.8791 g 0.8771 g 0.8961 g 0.8879 g(+)1.00% Sample 8 1.0042 g 0.9968 g 1.0130 g 1.0066 g (+)0.24% Mean wt.0.9157 g ± 0.1476 0.9181 g ± 0.1422 0.9255 g ± 0.1499 0.9261 g ± 0.1505(+)1.14%† positive change in mass = +‡ negative change in mass = −

TABLE 5 MTA Solubility Results MTA Wo(Initial Total Change in weight) T₁T₇ T₂₁ Mass (To-T₂₁) Sample 1 0.8715 g 0.8611 g 0.8797 g 0.8807 g(+)1.04% Sample 2 0.7351 g 0.7269 g 0.7467 g 0.7515 g (+)2.18% Sample 30.8607 g 0.8516 g 0.8716 g 0.8773 g (+)1.66% Sample 4 0.9702 g 0.9569 g0.9602 g 0.9646 g (−)0.58% Sample 5 0.9813 g 0.9579 g 0.9578 g 0.9759 g(−)0.55% Sample 6 0.8139 g 0.7920 g 0.7958 g 0.8128 g  (−)0.135% Meanwt. 0.8721 g ± 0.1370 0.8577 g ± 0.1308 0.8686 g ± 0.1219 0.8771 g ±0.1256 (+)0.57%† positive change in mass = +‡ negative change in mass = −

The change in mass for each of the samples revealed that there was atendency for a positive gain in total mass (+0.024%-+2.46%) with a meangain in mass of 1.14% over the 21 day period for CMMTA samples.Likewise, half of the MTA samples (1-3) revealed a positive change inmass (+1.04%-+2.18%) while samples 4-6 showed a negative change in mass(−0.135%-−0.58%) with an overall mean gain in mass of 0.57% over the 21day period for the MTA samples. When examining differences between thetwo groups, the Mann-Whitney U-test displayed no significant differencesbetween MTA and CMMTA in solubility (P<0.05). Furthermore, statisticalanalysis with the Wilcoxon signed ranks test was unable to show astatistical significant difference when the mean weight of the specimenswere compared at different time intervals (T₁, T₇, and T₂,) (P<0.05).

Dispersion Resistance/Washout

Weights (g) of each test group with corresponding repeated measures onwashout for Portland cement, MTA, and CMMTA is shown in Tables 4-6respectively. Results from the Friedman test used to analyze the amountof cumulative washout revealed a significant difference observed betweengroups (P<0.05). However, due to the small sample size, Post Hocanalysis (Median test) was unable to identify significant differenceswithin groups. TABLE 6 Washout Results for Portland cement Group 1(Portland cement) Cumulative Mi (Initial Percent weight) Mf(1) Mf(2)Mf(3) Washout Test #1 21.3368 g 20.9374 g 20.8175 g 20.7019 g (−)2.9756%Test #2 21.9530 g 21.5350 g 21.5632 g 21.4968 g (−)2.0781% Mean 21.6449g 21.2362 g 21.1904 g 21.5994 g (−)2.5269%† positive change in mass = +‡ negative change in mass = −

TABLE 7 Washout Results for MTA Group 2 (MTA) Cumulative Mi (InitialPercent weight) Mf(1) Mf(2) Mf(3) Washout Test #1 20.9886 g 20.4855 g20.4103 g 20.2767 g (−)3.3918% Test #2 21.4967 g 20.9457 g 20.7365 g20.6874 g (−)3.7647% Mean 21.2427 g 20.7156 g 20.5734 g 20.4821 g(−)3.5783%† positive change in mass = +‡ negative change in mass = −

TABLE 8 Washout Results for Chemically Modified MTA Group 3 (CMMTA)Cumulative Mi (Initial Percent weight) Mf(1) Mf(2) Mf(3) Washout Test #121.6637 g 21.8742 g 22.0083 g 22.0091 g (+)1.5944% Test #2 22.0066 g22.3133 g 22.2567 g 22.2500 g (+)1.1060% Mean 21.8352 g 22.0938 g22.1325 g 22.1296 g (+)1.3502%† positive change in mass = +‡ negative change in mass = −

Dye Leakage

An apicoectomy followed by a root-end filling material is a commonendodontic procedure used to rectify recalcitrant periapical pathosis inteeth where orthograde endodontic therapy has failed and nonsurgicaltreatment is not an option. One of the properties of an ideal root-endfilling material is the ability to seal the root canal system (2). Dyeleakage studies are a quick an effective method to evaluate the sealingability of root-end filling materials (22). In 1989, Kersten and Moorerdetermined the leakage of methylene blue to be comparable to that of asmall bacterial metabolic product of similar molecular size. Thus, whena filling material does not allow the penetration of small moleculessuch as methylene blue, it has the potential to prevent leakage oflarger substances such as bacteria and their by-products (24). Under theparameters of this study, leakage was quantified with the use of aLikert four-point scale in which 0=no dye penetration observed, 1=dyepenetration observed up to 1 of the cavity depth, 2=dye penetrationobserved between ½ but not beyond root-end filling material placement,and 3=dye penetration observed beyond the filling material and into thecanal system. Thus, greater disparity from a score of zero directlyreflects the ability of the root-end filling to adequately seal thedentin/material interface. Graphical representation of leakage scoresobtained over 72 hours is presented in Table 1. From this table, we wereable to conclude that the greatest disparity occurred between amalgamand CMMTA groups. A similar contrast was also evident between the MTAand amalgam groups. However, there was no significant difference notedin leakage between MTA and CMMTA groups.

Our results indicate that the CMMTA (1% methylcellulose+2% CaCl₂ in MTA)was comparable to the unaltered MTA (MTA/H₂O) in preventing dyepenetration beyond the extent of the material. Therefore, the additivesplaced into MTA had no significant effect on its sealing properties. Infact, the chemically modified MTA showed no evidence of leakage in all15 specimens.

Chemical Shrinkage

Numerous properties of cementitious materials are controlled by theirinitial hydration rate (early-age strength development, heat release,and crack resistance). A direct method for analysis of the cement'sinitial hydration rate is by quantifying the chemical shrinkage of thecement paste during its hydration. As cement hydrates, the hydrationproducts occupy less volume than the initial reacting materials (cementand water). As a result of this volume change, a hydrating cement pastewill absorb water, if available from its immediate surroundings. Atearly times this water absorption is in direct proportion to the amountof hydration that has occurred (25).

It has been generally considered that a potential root-end fillingmaterial should set as soon as it is placed in a root-end cavity withoutsignificant shrinkage. This would allow for dimensional stability of thematerial after placement and less time for an unset material to be incontact with periapical tissues. The incorporation of 1%methylcellulose+2% CaCl₂ into MTA by Ber. (18) has demonstrated to showpromise to rectify some of MTA's potential shortcomings as a root-endfilling material (long setting time and poor handling characteristics).A detrimental effect of calcium chloride is drying shrinkage (26). Thisstudy was undertaken to determine if the incorporated additives (namelyCaCl₂) into MTA significantly affected the chemical shrinkage propertiesof MTA.

Statistical analysis in the mean amount of chemical shrinkage occurringover 1 week (168 hours) for each of the six groups revealed nosignificant difference between groups at any of the determined timeintervals (P<0.05). As illustrated in FIG. 8, specimens with thegreatest to the least amount of chemical shrinkage displayed over 1 weekis represented as follows: Group 5 (2% CaCl₂ in PC)>Group 6 (1% MC+2%CaCl₂ in PC)>Group 1 (PC/H₂O)>Group 4 (2% CaCl₂ in MTA)>Group 2(CMMTA)>Group 3 (MTA/H₂O). We expanded the graph to provide a clearerrepresentation of specific trends for each specimen tested relative toearly age shrinkage (T₀-T₈) (FIG. 9). Both figures illustrate aconsistent increase in chemical shrinkage for each of the specimenstested over time. Likewise, the addition of 2% calcium chloride revealeda propensity to increase the chemical shrinkage rate. This is expected,since calcium chloride is used as an accelerant to increase thehydration process and provide early-age strength. Nonetheless,statistical analysis was able to demonstrate no significant amount ofshrinkage between MTA and CMMTA mean samples.

These results have demonstrated that unique to the dental sector andunlike in the cement industry, small quantities (usually <1 gram) of MTAmixed at a 3:1 w/c ratio placed in intimate contact with periapicaltissues which provides 100% humidity within an aqueous environment willenable and maintain saturation of the material and prevent a significantamount of autogenous or drying shrinkage.

Solubility

Root-end filling materials used during periapical surgery are routinelyplaced in intimate contact with inflamed or infected areas of theperiodontium. It is therefore essential that the root-end fillingmaterial be given every opportunity to maintain its apical seal andresist dissolution while in the presence of moisture/blood or lowered pHof the involved area. Torabinejad et al. was able to demonstrate thatMTA leaked significantly less than amalgam, Super EBA and IRM in thepresence of blood, and they observed that the presence or absence ofblood had no significant effect on the amount of leakage of the material(27). The rationale for this is that MTA beneficial properties arerealized with the added moisture from blood within the surgical siteduring the hydration process to initiate the initial seal. Theliterature states the presence of periradicular inflammation may providean acidic pH of 5.5 and this lowered pH may alter the physicalproperties of MTA to inhibit setting reactions, affect adhesion, orincrease solubility of the material (28). A study performed by Roy etal. was able to demonstrate that the sealing ability of freshly mixedMTA was not affected in an acidic environment (pH 5.0) (29). Conversely,a study performed by Lee et al. was able to make evident that an acidenvironment of pH 5 adversely affected the physical properties and thehydration behavior of MTA by retarding the dissolution of reactants,(C₃S, C₂S, and C₃A) therefore decreasing the production of Portlanditecrystals. Furthermore, SEM and XRD analysis also revealed that thelowered pH had potentiated a decreased hardness value of MTA withdissolution of surface crystals (30).

The inventors observed that the addition of 1% MC and 2% CaCl₂ into MTAhad no detrimental effects on the material's solubility. Under theparameters used in this example, all specimens were immersed indistilled H₂O for 21 days to provide an adequate timeframe to identifytrends in the initial solubility that may affect long-term results.Thus, if the material would show any initial dissolution, there would bea chance that the marginal seal has been disrupted and the potential forleakage to occur.

From the observations, it appears that specimens from both CMMTA and MTAgroups showed no or minimal signs of solubility in water over theobservation time. In fact, CMMTA and MTA groups both demonstrated meanincreases in water absorption over the 21 day period respectively(+1.14% and +0.57%). Our results were somewhat surprising to see apositive change in mean mass for both groups over this timeframe. Onemay direct this discrepancy to standard measuring error where thespecimens were weighed to 0.0001 grams. It is also plausible,methylcellulose, which is traditionally used as a bulking agent in themarketplace, may have potentially absorbed additional water into thecement during the hydration process adding to the higher mean increasein weight of CMMTA. Nonetheless, these results are in agreement with astudy performed by Torabinejad, (22) who concluded that MTA, Super-EBA,and amalgam showed no signs of solubility at 21 days.

Clinically, there is no standard method for predictably measuring themanufacturer's recommended 3:1 w/c ratios for MTA. Fridland (31) wasable to demonstrate that the degree of solubility in MTA increased asw/c ratio increased. Therefore, the amount of water used in preparingthe mix has a direct effect on solubility when the material is incontact with an aqueous environment. This increase in solubility has thepotential to affect the long-term seal that can essentially lower theoverall success of the endodontic procedure.

Our data is in opposition to a recent study performed by Fridland (32).This long-term study measured solubility over 78 days with varying w/cratios. The authors concluded that MTA with a 0.33 w/c ratio over 78days revealed a 24.04% cumulative solubility of the material's initialdry weight. The disparity in solubility results between studies couldhave resulted from differences in measurement methodology. Fridland etal. calculated solubility according to an amalgamation of ISO 6876standard (33) and ADA Specification #30 (34). In essence, Fridland etal. used an indirect weight measurement to determine the solubility ofMTA. These authors used values from the weighted residues as apercentage of the initial dry weight of the specimens. In contrast, ourmethodology mirrored a study performed by Torabinejad, (22) who used amodification to ADA Specification #30 using direct measurement of thespecimens at the dedicated time intervals.

Dispersion Resistance/Washout

During periapical surgery, root-end filling materials are inevitablyexposed to periapical tissues and fluids. This continuous moisturecontamination may complicate the placement of an effective seal andplace the material at risk to washout of the material. This isparticularly relevant for freshly placed MTA because of its lengthysetting time (165 minutes) (22).

MTA seems to have similar vulnerabilities to washout as Portland cementwhen placed in aqueous environments with prolonged setting times. Thecement industry routinely deals with wet conditions (underwater concreteplacement) that can potentially affect the properties of the material,not unlike conditions encountered during periapical surgery. For adiscussion of how the cement industry addresses problems of wetconditions, see Concrete Construction Engineering Handbook, E. Nawy,ed., New York, CRC Press, 1997; Concrete Construction Handbook, J.Dobrowski, 4^(th) ed., New York, McGraw-Hill, Inc., 1998; and Kosmatkaand Panarese, Design and Control of Concrete Mixtures, 13 th ed.,Portland Cement Association, Skokie, Ill., 1988, all of which are hereinincorporated by reference. To address these problems for dentalapplication, an anti-washout mixture (methylcellulose) is added to thecement to facilitate a more cohesive cement. The addition of thisadditive increases the viscosity of the water used in the mixture,therefore, producing a more thixotropic material to resist washout.Clinically, most of the disintegration of the cement will initiallyoccur during the placement of the material and not once it has set. Thatis why the addition of this cohesive antiwashout material may inhibitthe dispersion of material from the cavity both during placement and aswell as the first few hours of setting.

The inventors (18) have adopted the cement industry's solutions to theseproblems with the addition of 1% methylcellulose+2% CaCl₂ in MTA. Theinventors evaluated in this example whether the chemically modified MTAhas provided added benefits to the parent cement (MTA) in terms ofwashout resistance. The results obtained in this study landed within thetypical performance requirements for allowable washout (<6-12%) ofunderwater concrete for all of the specimens tested (34). Indeed, ourresults from the Friedman test used to analyze cumulative washoutrevealed a significant difference observed between groups (P<0.05). Whenevaluating the data mathematically, one could arrive at a conclusionthat the significant difference in mean cumulative washout was betweenGroup 2 (MTA=−3.57%) and Group 3 (CMMTA=+1.34%). As in the solubilitystudy, we would expect to see a negative washout value for CMMTA. Thepositive cumulative washout for CMMTA could possibly be explained bystandard measuring error of the materials during the weight measurementprocess or inadequate removal of H₂O from the receiving container priorto measurement.

In conclusion, the data presented in this example support our positionthat the addition of 1% MC+2% CaCl₂ into MTA has not deleteriouslyaltered any of the parent cement's additional physical properties(marginal leakage, chemical shrinkage, cement solubility, and washoutresistance). On the contrary, the results from the four studies testingthe physical properties of CMMTA have concluded: Dye leakage resultsdemonstrated that there was no statistically significant differencenoted between CMMTA and MTA samples (P<0.05). In addition, we were ableto demonstrate significantly less leakage between the CMMTA and MTAgroups compared to amalgam (P<0.05). Chemical shrinkage results reportedno statistically significant difference noted between any of the groupsat any of the designated timeframes (T₁, T₂, T₃, T₂₄, and T_(w)). Moreimportantly, we were able to show no statistically significantdifference in mean chemical shrinkage between CMMTA and MTA samples atany of the designated time intervals of the specimens (P<0.05). Cementsolubility results revealed no statistically significant differencebetween CMMTA and MTA groups (P<0.05). Furthermore, we were able to showno significant difference between weights of the test materials atdifferent time intervals. Modified washout tests indicated a significantdifference observed between groups 1-3 (P<0.05). Data obtained from thestudy demonstrated CMMTA as having the most mean cumulative washoutresistance while MTA displayed the least cumulative washout resistance.However, there were no significant differences noted between these twogroups (P<0.05).

The following references are cited throughout this section using therelated parenthetical numbering system. The references are incorporatedherein by reference. Applicant reserves the right to challenge theveracity of statements made therein.

1) Sarkar N K, Caicedo R, Ritwik P, Moiseyeva R, Kawashima I.Physicochemical basis of the biologic properties of mineral trioxideaggregate. J Endod. 2005; 31:97-100.

2) Gartner A H, Dom S O. Advances in endodontic surgery. Dent Clin NorthAm 1992; 36:357-78.

3) Koh E T, Torabinejad M, Pitt Ford T R, Brady K, McDonald F. Mineraltrioxide aggregate stimulates a biological response in humanosteoblasts. J Biomed Mater Res. 1997; 37:432-9.

4) Koh E T, McDonald F, Pitt Ford T R, Torabinejad M. Cellular responseto Mineral Trioxide Aggregate. J Endod 1998; 24:543-7.

5) Torabinejad M, Hong C U, Pitt Ford T R, Kaiyawasama S P. Tissuereaction to implanted super-EBA and mineral trioxide aggregate in themandible of guinea pigs: a preliminary report. J Endod 1995; 21:569-71.

6) Torabinejad M, Ford T R, Abedi H R, Kariyawasama S P, Tang H M.Tissue reaction to implanted root-end filling materials in the tibia andmandible of guinea pigs. J Endod 1998; 24:468-71.

7) Pitt Ford T R, Torabinejad M, Abedi H R, Bakland L K, Kariyawasama SP. Using mineral trioxide aggregate as a pulp-capping material. J AmDent Assoc 1996; 127:1491-4.

8) Osorio R M, Hefti A, Vertucci F J, Shawley A L. Cytotoxicity ofendodontic materials. J Endod 1998; 24:91-6.

9) Keiser K, Johnson C C, Tipton D A. Cytotoxicity of mineral trioxideaggregate using human periodontal ligament fibroblasts. J Endod 2000;26:288-91.

10) Torabinejad M, Rastegar A F, Kettering J D, Pitt Ford T R. Bacterialleakage of mineral trioxide aggregate as a root-end filling material. JEndod 1995; 21:109-12.

11) Wu M K, Kontakiotis E G, Wesselink P R. Long-term seal provided bysome root-end filling materials. J Endod. 1998; 24:557-60.

12) Torabinejad M, Watson T F, Pitt Ford T R. Sealing ability of amineral trioxide aggregate when used as a root end filling material. JEndod. 1993; 19:591-5.

13) Martell B, Chandler N P. Electrical and dye leakage comparison ofthree root-end restorative materials. Quintessence Int. 2002; 33:30-4.

14) Torabinejad M, Higa R K, McKendry D J, Pitt Ford T R. Dye leakage offour root end filling materials: effects of blood contamination. J Endod1994; 20:159-63.

15) ProRoot® MTA, Product Literature, Dentsply Tulsa Dental, Tulsa,Okla. 74136.

16) Deal B, Wenkus C, Johnson B, Fayad M. Chemical and physicalproperties of MTA, Portland cement, and a new experimental material,fast-set MTA. J Endod 2002; 28:252.

17) Lee E S. A new mineral trioxide aggregate root-end fillingtechnique. J Endod 2000; 26:764-5.

18) Ber, B S. “Manipulation of Handling Characteristics of MTA,”Master's Thesis, Saint Louis University, 2004.

19) M. Geiker, Studies of Portland Cement Hydration: Measurements ofChemical Shrinkage and a Systematic Evaluation of Hydration Curves byMeans of the Dispersion Model. Ph. D. Thesis, Technical University ofDenmark, 1983.

20) Proposed test method ASTM CXXXX Test method for chemical shrinkageof hydraulic cement paste. ASTM Committee C-1. Subcommittee C01.31 onvolume change.

21) ANSI/ADA. Revised American National Standard/American DentalAssociation Specification No. 30 for dental zinc oxide eugenol cementsand zinc oxide noneugenol cement 7.5, 2000.

22) Torabinejad M, Hong C U, McDonald F, Pitt Ford T R. Physical andchemical properties of a new root-end filling material. J Endod 1995;21:349-53.

23) Proposed test method ASTM CXXXX Test method for chemical shrinkageof hydraulic cement paste. ASTM Committee C-1. Subcommittee C01.31 onvolume change.

24) Kersten H W, Moorer W R. Particles and molecules in endodonticleakage. Int Endod J. 1989; 22:118-24.

25) Parrott L. J, Geiker M, Gutteridge W. A., Killoh D., MonitoringPortland cement hydration: comparison of methods. Cement and ConcreteResearch. 1990; 20:919-926.

26) Kosmatka, Steven H., and Panarese, William C. Design and Control ofConcrete Mixtures, 13th ed., PortlandCement Association, Skokie, Ill.1988.

27) Torabinejad M, Higa R K, McKendry D J, Pitt Ford T R. Dye leakage offour root end filling materials: effects of blood contamination. J Endod1994; 20:159-63.

28) Malamed S. Chapter 16. In: Local anesthetic considerations in dentalspecialties: handbook of local anesthesia. 4th edn. St. Louis: Mosby;1997; p. 232.

29) Roy C O, Jeansonne B G, Gerrets T F. Effect of an acid environmenton leakage of root-end filling materials. J Endod 2001; 27:7-8.

30) Lee Y L, Lee B S, Lin F H, Yun Lin A, Lan W H, Lin C P. Effects ofphysiological environments on the hydration behavior of mineral trioxideaggregate. Biomaterials. 2004; 25:787-93.

31) Fridland M, Rosado R. Mineral trioxide aggregate (MTA) solubilityand porosity with different water-to-powder ratios. J Endod. 2003;29:814-7.

32) Fridland M, Rosado R. MTA Solubility: A Long Term Study. J Endod.2005; 31:376-379.

33) International Organization for Standardization. Specification fordental root canal sealing materials. ISO 6876. London: British StandardsInstitution, 2001.

34) ANSI/ADA. Revised American National Standard/American DentalAssociation Specification No. 30 for dental zinc oxide eugenol cementsand zinc oxide noneugenol cement 7.5, 2000.

35) Department of the Army EC 1110-2-6052. U.S. Army Corps of EngineersCECW-EI Washington, D.C. 20314-1000. 2001; Appendix B-6.

1. A dental repair composition comprising a dental repair compound, adivalent cation—halogen salt and a cellulose-derivative polymer, whereinthe composition has higher viscosity and lower setting time relative tothe dental repair compound without the divalent cation—halogen salt andthe cellulose-derivative polymer.
 2. The dental repair compositionaccording to claim 1, wherein the dental repair compound is a mineraltrioxide aggregate (“MTA”) or a Portland cement.
 3. The dental repaircomposition according to claim 1, wherein the divalent cation—halogensalt is calcium chloride.
 4. The dental repair composition according toclaim 1, wherein the cellulose-derivative polymer is methyl-cellulose.5. The dental repair composition according to claim 1, wherein thedivalent cation—halogen salt concentration is between 0.1% and 20% byweight inclusively.
 6. The dental repair composition according to claim1, wherein the cellulose-derivative polymer concentration is between0.1% and 20% by weight inclusively.
 7. A compound additive consistingessentially of a divalent cation—halogen salt and a cellulose-derivativepolymer, whereby upon addition of the compound additive to a dentalrepair compound a compound admixture is created, the compound admixturehaving a shorter setting time and a higher viscosity than the dentalrepair compound.
 8. The compound additive according to claim 7, whereinthe cellulose-derivative polymer is at a concentration of between 0.1%and 50% inclusively by weight.
 9. The compound additive according toclaim 7, wherein the divalent cation—halogen salt is at a concentrationof between 0.1% and 55% inclusively by weight.
 10. The compound additiveaccording to claim 7, wherein the dental repair compound is any one ofeither Portland cement or MTA.
 11. The compound additive according toclaim 7, wherein the divalent cation—halogen salt is calcium chloride.12. The compound additive according to claim 7, wherein thecellulose-derivative polymer is methyl-cellulose.
 13. A method ofproducing a compound additive, the compound additive comprising adivalent cation—halogen salt and a cellulose-derivative polymer, themethod comprising the steps of a. combining 3 parts divalentcation—halogen salt with 1 part water by weight to produce a saltsolution, then b. heating one half of the solution to 80° C. and keepingone half of the solution at room temperature, then c. combining 3 partscellulose-derived polymer to 4 parts of the one half of the solutionthat was heated to 80° C. by weight to produce a warm salt-polymersolution, then d. combining the one half of the solution at roomtemperature to the warm salt-polymer solution to produce a homogeneousmixture, then e. allowing the homogeneous mixture to thicken by chillingthe homogeneous mixture, then f. stirring the homogeneous mixture for aneffective amount of time to create a homogenous gel, the homogeneous gelbeing the compound additive.
 14. A method of producing the dental repaircomposition of claim 1, the method comprising the steps of: a. producinga compound additive according to the method of claim 13, then b.combining the compound additive with a dental repair compound.
 15. Amethod of filling a tooth cavity, comprising the steps of a. identifyingthe cavity of the tooth to be filled; b. preparing the tooth to befilled, c. preparing a dental repair composition as set forth in claim14, d. introducing the dental repair composition into the tooth cavitywhereby the path of communication between a inner portion of the cavityand the outer surface of the tooth is sealed.
 16. A method of treatingtooth decay, comprising the steps of: a. identifying the decay; b.removing the decay to create a cavity to be filled; c. preparing adental repair composition according to claim 14; and d. introducing thedental repair composition into the cavity whereby the path ofcommunication between an inner portion of the cavity and the outersurface of the tooth is sealed.
 17. A method of performing root canaltherapy on a tooth, comprising the steps of: a. removing a portion ofthe tooth to expose the root canal, b. preparing the root canal to befilled; c. preparing a dental repair composition according to claim 14;and d. introducing the dental repair composition into the root canalwhereby the path of communication between the root canal and the outersurface of the tooth is sealed.
 18. A method of apicoectomy on a toothcomprising the steps of a. removing the apex of a root of the toothwhereby the root canal of the tooth is exposed, b. preparing a root endcavity in the tooth; c. preparing a dental repair composition accordingto claim 14; and d. filling the root end cavity with the dental repaircomposition whereby the path of communication between the canal and theouter surface of the tooth is sealed.
 19. A method of sealing a rootperforation which has created a path of communication between a canal ofthe tooth and an outer surface of the tooth, said method comprising thesteps of a. identifying the root perforation; b. preparing the rootperforation for placement of a dental repair composition therein c.preparing a dental repair composition according to claim 14; and d.filling the root perforation with the dental repair composition wherebysaid dental repair composition seals the path of communication betweenthe outer surface of the tooth and the canal of the tooth.
 20. A kitcomprising a dental repair compound in a first package, a compoundadditive according to claim 8 in a second package, and a set ofinstructions.